Excitation system for mercury arc rectifiers



March 1937- A. L. ATHERTON ET AL 2,075,011

EXCITATION SYSTEM FOR MERCURY ARC RECTIFIERS Filed July 12, 1933 5 Sheets-Sheet l INVENTOR Alfi'ea LAX/7971072 4? Herbs A. Rose.

ATTORNEY Mar hso, 1937- A. L. ATHERTON ET AL 2,075,011

EXCITATION SYSTEM FOR MERCURY ARC RECTIFIERS Filed July 12, 1933 3 Sheets-Sheet 2 WITNESSES: INVENTOR 4g AlfreaL/lzfzerzon 2 Herbert A R05 6.

(1 M BY :ATTORNEY March 1937- A. L. ATHERTON ET AL 2,075,011

EXCITATION SYSTEM FOR MERCURY ARC RECTIFIERS Filed July 12, 1933 3 Sheets-Sheet 3 vllllllllllllllu I ?l// INVENTOR5 r/IZf//I///////////4 I WITNESSES:

M. 0 0 Y m 64 m m aw 6 WW Patented Mar. 30, 1937 UNITED STATES PATENT OFFICE Alfred L. Atherton, Verona, and Herbert A. Rose,

Pittsburgh, Pa.,

assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a. corporation of Pennsylvania Application July 12, 1933, Serial No. 680,160

1 Claim.

Our invention relates to an excitation system for a mercury arc rectifier.

In the operation of vapor electric devices such as mercury arc rectifiers, it has been found de- 5 sirable to provide the anodes with protective devices such as shields and grids. These devices not only prevent the formation of inverse arcs to the anodes by deionizing the arc space, but in addition have a detrimental effect in that they retard the formation of the desired current-carrying arcs, particularly when the rectifier is just being placed in service.

Various systems have heretofore been proposed for securing pick-up. In the main these have comprised a dual excitation system in which there is an ignition arc and a main exciting arc. When both arcs operate continuously the capacity of the excitation system is much increased resulting in serious decrease of emciency of the converting system. While if the ignition arc is extinguished it must operate to restrike whenever the exciting arc is extinguished resulting in multiplicity of control equipment with the ever present possibility of failure or faulty operation. In the system according to our invention, a starting electrode is placed adjacent the cathode surface and an excitation anode is placed adjacent the main anodes. A suitable source of direct current is connected to the starting anode and to the exciting anode with a voltage consuming device in series with the starting anode so that the major portion of the exciting current automatically transfers from the starting anode to the exciting anode. This system eliminates the losses of double excitation arcs without requiring any control equipment to reestablish the excitation are if for any reason it is extinguished. Accordingly, it is an object of our invention to provide an excitation system requiring a minimum of exciting current.

It is a further object to provide a system for transferring the exciting are from a starting anode to an excitation anode without the use of moving control equipment.

It is a further object to retain a small arc to the starting anode for stablizing the cathode spot.

Other objects and advantages of our invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Figure 1 is a sectional elevation of a rectifier embodying our invention, Fig. 2 is a plan view showing the relative 10- cation of the main anodes and the exciting anode according to our invention,

Fig. 3 is a view similar to Fig. 1 showing a modification according to our invention, and

Fig. 4 is a detailed illustration of the starting electrode assembly.

The apparatus according to our invention comprises an evacuated chamber I having a suitable cathode 2 and a plurality of main anodes 3. A starting anode assembly 5 is placed adjacent the central portion of the tank in such a position that a starting rod 6 may be projected into contact with the cathode 2 for initiating an exciting arc in the rectifier. When an exciting arc is established, the starting rod 6 is withdrawn into an auxiliary excitation anode head 1 and the exciting are transfers from the rod 6 to the auxiliary anode head I.

A second keep-alive or excitation anode I0 is placed adjacent the open end of one of the anode shields l2. Preferably the excitation anode is placed midway between two main anodes 3 and somewhat within the main anode circle, so that the excitation anode I0 is as close as is mechanically possible to the open ends of the shields enclosing two of the main anodes.

While any source of direct current may be used to provide the exciting current, we prefer to use a transformer l5 and a copper oxide rectifier It for securing suitable uni-directional current for the exciting anodes. Preferably, the exciting current source has a steep regulation effect so that the high light-load voltage is available for energizing the solenoid [8 for actuating the starting rod 6. When the starting rod 6 is projected into contact with the cathode 2, thereby short circuiting the starting solenoid l8, allowing the starting rod 6 to be withdrawn into the starting electrode 1, the current drawn by the starting arc will reduce the excitation voltage to a value insufficient to operate the solenoid IS.

The exciting current source is connected to the starting anode I through a suitable voltage consuming device such as a resistor 20 and to the excitation anode I0 through substantially no impedance. Consequently, there will be a difierence of potential between the starting anode I and the excitation anode H) which will cause the major portion of the keep-alive arc to transfer to the excitation anode l0 adjacent the main anodes 3.

While most of the current flows through the excitation anode III, a small portion will continue to flow from the starting anode head I. Consequently, if the exciting anode arc should,

for any reason, be extinguished, it would again restrike from the starting anode 1 without the necessity of operating the starting rod 6. Since the exciting anode It is not connected to the main rectifier power source, there is little danger of a destructive backfire tothe exciting anode I0. Consequently, the exciting anode l0 may be left unshielded and in condition to readily assume an exciting arc, which will produce ionization adjacent the mouth of the shields I! of the main anodes I.

In the modification according source of exciting current is directly connected to the tank wall so that the tank wall I serves as an exciting anode. In the operation of this modification, the exciting arc is started to the starting anode I in the usual manner and is transferred by the resistor or other voltage consuming device to the tank wall I. Since the arc from the tank wall to the cathode spot is considerably longer than the are from the cathode to-the starting anode I, and since the arc must necessarily originate in the vicinity of the main anodes 3, the are from the tank wall to the cathode 2 produces suflicient ionization adjacent the anode to Fig 3, the

shields II to permit pick-up oi the main anodes 3 when potential is applied thereto.

While we have shown and described a preferred embodiment of our invention, it is apparent that changes and modifications may be made therein without departing from the spirit and scope of our invention. We desire, therefore, that only such limitations be imposed as are embodied in the accompanying claim or as may be necessitated by the prior art.

' We claim as our invention:

A mercury-arc rectifier comprising an arc chamber, a vaporizable cathode therein, anode in said chamber, a shield about said anode, a starting electrode for initiating an arc in said rectifier. a second exciting electrode for producing ionization adjacent the open end of said ALFRED L. ATHERTON; HERBERT A. ROSE. 

